Until now, the conventional wisdom governing biological pest control called for releasing as many different natural predators as possible to suppress as many pests as possible. In one of the first field studies of its kind, a UC Davis scientist recently found that a greater variety of predators may not always mean better pest control. "My results suggest that, in some circumstances, one species of predator may be better than two," says zoology researcher David A. Spiller. "In some circumstances, it might be better to remove some predators, rather than introduce them." At a salt marsh on the northern shore of the San Francisco Bay Area complex, Spiller studied two species of spiders: Cyclosa turbinata and Metepeira grinnelli. When Cyclosa was the only spider species in experimental plots, the total number of spiders was higher than in plots with both species present. Spiller found that Metepeira frequently displaced and sometimes killed Cyclosa. Because Cyclosa consumed more small insects per capita than Metepeira, Spiller believes Cyclosa alone could control small insects better than both species together. "Preliminary experiments should be conducted to determine the optimal set of predators for biological control of a particular pest," Spiller says. Spiller recently reported his findings at the annual meeting of the Entomological Society of America.